1. Field of the Invention
The present invention relates to the detection of light scatter in a flow cytometer, and more specifically, it relates to the use of the flow stream of a flow cytometer as an optical waveguide.
2. Description of Related Art
Flow cytometry is a technique used to characterize and categorize biological cells and/or their contents, such as DNA, and record their distributions, including actual sorting of this biological material in some cases. The biological cells are present in an aqueous-based solution, even when the sample material is eluted from a polymer matrix, such as in sheath-flow detection in electrophoresis experiments. In flow cytometry, the experimenter shines one or more beams of light at the biological material in the aqueous stream and observes the elastically and inelastically scattered light. The inelastically scattered light which is of interest is usually just fluorescence. Variations in the cells or DNA cause variations in the scattered light and these variations allow the desired characterization and categorization. To quantify these variations, the scattered light must be collected. In general, less right angle scattered (RAS) light is produced than small angle scattered light. It is desirable to collect as much of the scattered light as possible in order to maximize the speed and sensitivity of the procedure.
In previously used flow cytometers, the right angle scattered light has been viewed perpendicularly to the liquid flow, typically using a high numerical aperture (NA) microscope objective lens or fiber optic. Highest quality microscope objectives have a "numerical aperture" of 0.6, which provides a subtended polar angle of 2.beta.=37.degree.(0.64 radians). Some of the difficulties associated with this approach include the very limited depth of field of high NA lenses, and the necessity to align precisely the exact focal point of the lens with the illuminated region of the flow stream.